A magnetic sensor device is a sensor device that uses a plurality of magnetoresistive elements for which the property of resistance value changes with change in magnetic flux density. In a magnetic sensor device for simultaneous multi-channel detection of a magnetic pattern included in a paper sheet-like medium such as paper currency and the like, the amount of magnetization of the magnetic pattern is minute, and thus in order to detect the magnetic pattern with good sensitivity, anisotropic magnetoresistive elements are used that have higher sensitivity than semiconductor magnetoresistive elements under a magnetic environment that all of the plurality of anisotropic magnetoresistive element are highly sensitive without magnetic saturation, and the paper sheet-like medium such as paper currency and the like is required to pass through the magnetically strong environment.
The sensing direction of the anisotropic magnetoresistive element is the short-side direction, and reading of magnetic ink is achieved by application of a bias magnetic flux density that most increases sensitivity in the detection direction. A magnetic sensor device that uses an anisotropic magnetoresistive element is disclosed in Unexamined Japanese Patent Application Kokai Publication No. 2012-255770 (Patent Literature 1).